In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam through a mask having a predetermined pattern, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film.
A resist material in which the exposed portions change and become soluble in a developing solution is called a positive-type resist, and a resist material in which the exposed portions change and become insoluble in a developing solution is called a negative-type resist.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a wavelength shorter than these excimer lasers, such as an F2 excimer laser, electron beam, extreme ultraviolet radiation (EUV), and X ray.
Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources.
As a resist material that satisfies these conditions, a chemically amplified composition is used, which includes a base material component that exhibits changed solubility in an alkali developing solution under the action of acid and an acid generator component that generates acid upon exposure.
For example, as a positive-type chemically amplified resist composition, a composition containing a resin component (base resin) which exhibits increased solubility in an alkali developing solution under the action of acid, and an acid generator is typically used. If the resist film formed using the resist composition is selectively exposed during formation of a resist pattern, then within the exposed portions, acid is generated from the acid generator component, and the action of this acid causes an increase in the solubility of the resin component in an alkali developing solution, making the exposed portions soluble in the alkali developing solution.
Currently, resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are widely used as the base resins for resists that use ArF excimer laser lithography, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 1).
On the other hand, as the acid generator used in a chemically amplified resist composition, numerous compounds have been proposed, including, for example, onium salt acid generators such as iodonium salts and sulfonium salts, oxime sulfonate acid generators, diazomethane acid generators, nitrobenzylsulfonate acid generators, iminosulfonate acid generators, and disulfone acid generators.
Further, besides the base resin and the acid generator, a chemically amplified resist composition also frequently includes an added nitrogen-containing organic compound such as an alkylamine or an alkyl alcohol amine. These nitrogen-containing organic compounds function as quenchers that trap the acid generated from the acid generator, thereby contributing to an improvement in the lithography properties and the like.
In recent years, the development of photodegradable bases that decompose upon exposure to light or other radiation as quenchers has progressed significantly. A photodegradable base included in a resist composition functions as a normal quencher in unexposed portions that are not exposed to light or radiation. On the other hand, in those portions that are exposed to light or radiation, the photodegradable base itself decomposes, resulting in a loss of the quenching function which means the concentration of acid within the exposed portions is maintained at an appropriate level, and is prevented from becoming too low. Patent Document 2 discloses a resist composition that includes, as structural components, a base component composed of a polymer having a repeating unit containing a cyclic carbonate ester structure, an acid generator, and an acid diffusion inhibitor having a carbamate ester structure.